Smallest undersized spare tire I can get away with?

N

nobb

New member
My OEM spare tire is 20 years old now and would probably be a good idea to replace. Contrary to people running full sized spares, I'm considering what the smallest spare size I can get away with. I keep my spare on the roof basket, so any tire width I can shave the better (weight and clearance in parkades/car washes). Obviously if I did have to use the spare I would make sure it goes on the front wheels only.

Anyone else run an undersized spare? 215/70R16 is the smallest truck tire size, should I go even smaller and consider passenger tire sizes? Any other problems I should be aware of?
 
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Why do you run it on the roof if you run a small spare? That's just extra weight on the roof...
 
I wouldn't have any qualms with a Passenger tire for a spare.

There are two possible issues with an undersized spare:

1) The VSC / Trac compare wheel speeds to activate. Now, I am sure the relatively difference in wheelspeed is not going to immediarly trigger the VSC, but it might change how it response at the threshold.

2) Even on the front and in 2WD, it is going to make the differential "differentiate." This wouldn't be a big deal going 10 miles to the tire shop after work. But, if you had a flat 200 miles from your destination on a road trip, it might cause the diff to overheat.

Of course, neither of these notions are substantiated, but they are something to consider.
 
I recently put a 245/75 16 on as my spare. Narrower tire, hardly any shorter than the stock 265/70 16's I have on. Helps 'pick up' the tire from hanging so low under the vehicle.
 
Lindenwood said:
2) Even on the front and in 2WD, it is going to make the differential "differentiate." This wouldn't be a big deal going 10 miles to the tire shop after work. But, if you had a flat 200 miles from your destination on a road trip, it might cause the diff to overheat.
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Good point. I guess only if you had manually locking hubs that you could stop the front differential from turning. This basically means it's risky to use a different sized spare on a 4wd vehicle.
 
Yet there are hundreds, if not thousands of 3rd gen T4R's rolling around with 285's and a 3" lift and still have the 265/70 spare underneath...just to put in perspective.
 
I've been considering the same thing, other than the roof thing. No room on the roof. I want to see if I can put a 265/75R16 under the back. I know it wont fit with the hitch. It's fairly close to 285/70r17. I don't think it would be an issue unless you have a limited slip. Just my thought. Hadn't really considered it much past that.
 
Can't you get a skinny tall tire that has the same diameter but isn't as wide so it doesn't stick up far off your roof?
 
265/75R16 fits under mine with the hitch. The narrower but same diameter 235/85R16 also fits and doesn't hang down as much. I wouldn't worry about the weight of carrying the spare on the roof either. I had a 300 pound roof top tent and it was a non issue.
 
blaze17 said:
265/75R16 fits under mine with the hitch. The narrower but same diameter 235/85R16 also fits and doesn't hang down as much. I wouldn't worry about the weight of carrying the spare on the roof either. I had a 300 pound roof top tent and it was a non issue.
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You can't say that adding 300 lbs to the roof of the vehicle won't change the dynamics of how it handles... A tire doesn't weigh near as much as a RTT, but it's still something to consider.
 
What is the weight difference between the smallest tire that works and the factory spare? maybe 30lbs? Weight on your roof is bad, but I feel like this is a lot of effort and has a lot of downsides for not much gain.
 
Unner said:
You can't say that adding 300 lbs to the roof of the vehicle won't change the dynamics of how it handles... A tire doesn't weigh near as much as a RTT, but it's still something to consider.
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After reading posts about people being scared by how their truck felt after mounting the spare on the roof I expected the RTT to be horrendous. I was was very pleasantly surprised. It still felt very stable both on the road and off camber off road. And this was when I had the front sway bar removed.
 
I cut out my rear cross member, added a new tube that sat higher up (due to body lift), and used a 235/85r16 as a spare for years. Never had to use it, but it was near the same 31 inch spare tire size, and was barely visible.

As other mentioned, if you run a small spare for a very short time, you'll be fine, but otherwise it will cause damage to the diff.

A family friend once went to get new tires at a tire shop, and ended up 285's on 3 corners and a 265 on the 4th. Needless to say, the diff locked up, and the shop ended up paying for a whole new diff.
 
Another note is that 235/85 is a stock size on full size trucks. Used tires for spares can be found reallllly cheap. I got myself a Cooper ST (I think? mud tire) for 50 bucks, still with the nipples.
 
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